FIG. 8 is a general sectional view of a gas turbine. In FIG. 8, reference numeral 31 is a first stage stationary blade, 32 is a flange of the stationary blade, and 33 is its support ring. Reference numeral 34 is a first stage moving blade, 35 is a second stage stationary blade, 36 is a second stage moving blade, 37 is a third stage stationary blade, 38 is a third stage moving blade, 39 is a fourth stage stationary blade, and 40 is a fourth stage moving blade. This example is composed of four stages of blades. One stationary blade is used in each stage. A moving blade is provided between two stationary blades through a disk in the rotor peripheral direction. Thus, a plurality of stationary blades and moving blades are disposed alternately in the axial direction.
In this gas turbine, in order to enhance the turbine efficiency, it is required to elevate the temperature of the working gas. In order to keep the temperature of the metal material of the wall for forming the gas passage below an allowable temperature of the material, holes for passing a cooling air are provided in these member so as to cool the member by passing cooling air. In FIG. 8, reference numeral 20 is a split ring provided in the wall around the first stage moving blade, in which a plurality of arc-shaped rings split on the circumference are coupled to compose a cylindrical wall, and a cooling air hole is provided to cool by passing cooling air.
FIG. 9 is an exploded view of portion B shown in FIG. 8 and shows the split ring in detail. In FIG. 8, the first stage moving blade 34 is disposed between the first stage stationary blade 31 and second stage stationary blade 35, and the split ring 20 is disposed around the circumference of the first stage moving blade 34. In FIG. 9, reference numeral 21 is a cooling air hole provided in the split ring 20. This cooling air hole 21 has an opening 21a inside in the upper face, and an opening 21b in the side face. Reference numeral 22 is an impinging plate. A cooling air inlet hole 23 is provided above the impinging plate 22 through which cooling air 50 is sent in. The cooling air 50 gets into an inner space 24, and reaches the split ring 20 after passing through the many holes provided in the impinging plate 22. This cooling air cools the surface of the split ring 20, and further flows into the cooling air hole 21 through the opening 21a, and flows out to the outside gas passage through the opening 21b, thereby cooling the inside of the split ring 20 in this process.
FIG. 10 is a view when seen along the arrows C--C in FIG. 9. This figure shows a part of the split ring 20. The diagram shows the split ring 20 forming a part of the cylindrical structure. Many cooling air holes 21 are arranged in the cylindrical side face. The cooling air holes 21 have opening 21b. The inside of the split ring 20 can be cooled by passing cooling air in these holes. The split ring 20 is coupled with adjacent split rings 20a, 20b and arranged cylindrically, and grooves 26a, 26b are provided alternately at the connection area, and a seal plate 25 is inserted into the grooves 26a, 26b, thereby preventing leakage of sealing air.
FIG. 11 is a view when seen along the arrows D--D in FIG. 10. This figure shows a state in which the seal plate 25 is inserted in the grooves at the ends as mentioned above to seal, multiple cooling air holes 21 are formed inside the split ring 20, and the cooling air holes 21 have openings 21a at the surface at one side, and openings 21b at the side face at the other side, and the cooling air is introduced from the openings 21a, and flows out to the gas pass from the openings 21b, thereby cooling the wall of the split rings 20.
FIG. 12A and FIG. 12B are magnified views of the seal plate shown in FIG. 10. FIG. 12A is a side view, and FIG. 12B is a view when seen along the arrows E--E in FIG. 12A. As shown in these figures grooves 26a, 26b are provided in the mutually adjacent split rings 20b and 20a, and the seal plate 25 is inserted in these grooves. As shown in FIG. 12A, the portions X and Y are groove processed parts of the seal plate 25, and cooling air holes cannot be easily provided in these portions. Consequently, cooling is not sufficient, and the high temperature gas is likely to stay in the space Z between the portions X and Y. Therefore, the portions X and Y are likely to be burnt by the high temperature gas.
FIG. 13A and FIG. 13B show burnt portions X, Y shown in FIG. 12. FIG. 13A is a sectional view, and FIG. 13B is a view when seen along the arrows F--F in FIG. 13A. As shown in these figures, the portions X, Y are exposed to the high temperature gas, and get burnt as indicated by 50, 51. When this state advances, the lower ends of the grooves 26a, 26b are lost, and the seal plate 25 provided inside may slip out. It has been hence demanded to develop a cooling structure capable of preventing burning of end portions at the connection area of such split ring.
Thus, in the connection area of the conventional gas turbine split rings, it is designed to seal the connection area by the seal plate, and the end portions of such connection area in which grooves are formed for inserting the seal plate are exposed to high temperature combustion gas and burnt, or reduced in wall thickness due to high temperature oxidation, or the end portions are melted and lost, and the seal plate in the grooves may slip out.